This invention relates to apparatus for and methods in brachytherapy. More in particular, this invention relates to brachytherapy apparatus and methods for high precision implantation of antitumor agents and other devices used in brachytherapy in a patient""s body.
In the field of medicine, nuclear radiation may be used for diagnostic and therapeutic treatment of patients inflicted with cancer. Typically, more than half of these patients need radiation therapy either as a primary or as adjunct mode of treatment. Conventional medical radiation sources used in these treatments include large fixed-position machines such as linear accelerators, as well as small, transportable radiation generating probes which provide a boost therapy. In the latter treatment system, miniaturized probes capable of producing a high dose of radiation in a pre-defined geometry (seeds) are inserted into a treatment volume. This treatment is commonly referred to as brachytherapy because the radiation source is located close to or, in some cases, within the treatment volume.
The advantage of brachytherapy is that very high doses of ionizing radiation are delivered to a localized volume of tissue such that the radiation is supplied primarily to the treatment volume without significantly affecting tissues in adjacent volumes. This ability, when combined with a rapid reduction in the radiation dose as a function of distance, shields distant anatomies from spurious radiation. Hence, the technique has provided excellent results for localized control of various tumors.
In applications where tumors under treatment are in the patient""s prostate gland, an applicator such as a perineal template is commonly employed with one or more probes that contain seeds or radiation sources. The template has an array of openings for accepting a plurality of sequential tandem brachytherapy probes or needles. During operation, the template is positioned near tumors to be treated and referenced to one or more scanned images before the seeds are inserted into the openings. For anatomical regions where there is no body cavity, the interstitial implantation of radioactive needles is preferred. The needles are typically long and hollow with small outer diameter and at least one sharp end to allow penetration through the tissue. Small gauge needles can deflect as they encounter obstructions such as calcification or changes in tissue impedance. A needle is easily bowed by a small bone.
During a brachytherapy operation, a physician needs to know the exact position of the seeds, as well as the radiation dosage distribution from these seeds. It is also desirable to quantify the radiation received by the surrounding organs. Images of the treatment area are obtained from modalities such as X-ray radiograph, computed tomography, magnetic resonance, ultrasound, or nuclear medicine scans of the patient during a treatment simulation procedure. The information obtained from the images is correlated with the position of the template or the needles for intracavity or interstitial treatment. The position of the seed inside the patient is determined relative to the needle and the template as a function of the needle length and orientation, minus a length of a remaining needle portion outside the template.
The radiation dose is computed by a dosimetry program by taking into consideration the intensity of the radioactive sources and their coordinates relative to the tumor. Needle bowing and deflection introduce errors in the coordinates of the radioactive seeds and results in miscalculation of the radiation dose. Implications of the error in the radiation dose calculation include underexposure of the tumor and exposure of normal tissue to harmful radiation.
In addition, bending of the needle may result in breaking of the needle in the tissue. This can cause tissue damage and may require surgery to remove the broken needle pieces.
It is therefore an aspect of some embodiments of this invention to provide an improved brachytherapy apparatus with which the bending and bowing of needle can be minimized or obviated such that the operator can correctly estimate the position of its tip from the portion of the needle outside the tissue.
It is another aspect of some embodiments of this invention to provide brachytherapy methods by which seeds and other kinds of brachytherapy devices can be deposited precisely where they are intended, mutually separated by specified distances and mutually in specified orientations.
A brachytherapy apparatus embodying this invention may be characterized as comprising a tubular needle, a holder supporting the needle and a driver for electromechanically causing the needle to move in its longitudinal direction inside a patient""s tissue. In order to prevent deflection and bowing of the needle when it encounters an obstruction such as a calcification, the tip of the needle is serrated, or provided with two or more cutting edges which may be triangular, protruding forward and the driver serves to cause a rotary and/or longitudinal motion of the needle. The rotary motion may be continuous or periodic. A periodic rotary motion may be provided by means of a piezoelectric hammer with a handle striking an anvil attached to a main body securely holding the needle. A piezoelectric tamper, similarly structured, may be used to provide the needle with a reciprocating longitudinal motion. After it is ascertained that the tip of the needle has arrived at a specified target position inside the patient""s tissue, a radioactive seed or whatever small object to be implanted in the patient tissue for brachytherapy is passed through the needle and pushed out thereof by a pusher, as the needle is slightly retracted to leave a track inside the tissue. Thereafter, a quickly hardening liquid may be injected through the needle to immobilize the deposited brachytherapy device. If desired, the needle may be retracted by a specified distance and another brachytherapy device may be similarly pushed through and out of the needle.
When a plurality of brachytherapy devices are deposited in a tissue, these devices may be preliminarily formed into a unit, fixed inside a hardened liquid so as to be linearly arranged and mutually separated by specified distances. Such a unit may be pushed through and out of a needle inserted into a patient""s body. Alternatively, the needle may be retracted from the target position to leave a track, or a groove, inside the tissue and a plurality of brachytherapy devices may be injected through the needle into this track together with a quickly hardening liquid.
By using an apparatus and method embodying this invention, a needle can be reliably inserted into a patient""s body without being deflected or bowing so as to have its front opening correctly positioned and brachytherapy devices can be deposited accurately where they are intended to be.